The first challenge for the Jackson Wastewater Treatment Plant was to reduce energy use by 10 percent. With that achieved, the goal was to treat each gallon 40 percent more efficiently.
The plant exceeded that goal by nearly two times and ahead of schedule. Now Johnny Ziem, wastewater manager, is looking to keep moving the bar and achieve net zero energy at the 5 mgd design/2.2 mgd average lagoon treatment plant in scenic Jackson Hole, Wyoming.

Water mixing

The latest project, installed in summer 2015, is a GridBee mixing system (Medora Corporation) to improve lagoon aeration efficiency. “We were operating 750 hp of aeration/mixing equipment, and we are now running 250 hp,” says Ziem. “This helped reduce our carbon footprint by about 1 million kWh. Even with the low power cost of 4.3 cents per kWh, we saved about $55,000 the first year alone.”

The $561,000 project was funded by the town of Jackson with help from the non-profit Teton County Wastewater Funds and Energy Conservation Works. Lower Valley Energy gave the township a rebate check of $224,592, covering about 40 percent of the project cost. Including the rebate and first-year savings the payback appears to be six years or less as the system is fine-tuned.  

The mixers are the latest in a list of projects that started when the town council looked at its operations in 2006 and decided to cut overall energy use by 10 percent by 2010, called the 10x10 Initiative. “That was a really good start on this path of really watching our energy, tweaking our use, looking at multiple ways we can save energy that also allows us to avoid some major costs,” says Ziem.

Going solar

In 2008, the plant installed 144 panels in a 27 kW solar array from Creative Energies in Lander, Wyoming. Two years later, a second phase added 702 panels for an additional 165 kW. “At the point, we had the biggest solar farm in Wyoming,” notes Ziem. More solar was to come, but not before the plant took other actions to become more efficient.

In 2010, old floating mixers that aerated five of the ponds were upgraded to Triton Aire-02 mixers (Aeration Industries) that mix much more efficiently and use less energy. That enabled the plant to meet its original goal of 10 percent energy savings.

The next year, to further reduce electricity use during part of the year, the plant got to work on the two 250 hp blowers for the coarse-bubble diffusion system in the second five lagoons. The plant added a high-speed turbo-blower from HSI (Atlas Copco) for aeration in the five winter months when less air is needed.

Around that time the town board issued a new challenge: The 40x20 Initiative directed the plant was to be 40 percent more efficient by 2020 than in 2006.

Better lagoons

In 2013, when Ziem moved from senior wastewater operator to his present position, the group changed the way the lagoons operated. The plant sometimes exceeded its permit maximum pH of 9 in summer and early fall when the lagoons produced substantial amounts of algae.

“Producing algae uses up a lot of alkalinity,” says Ziem. “We had the capability to bypass four of the five ponds that were on the diffuser system, and to shut off the air to the last pond and turn that into a polishing pond to try to regain some alkalinity.”

Doing so also enabled the two blowers to be shut down at intervals instead of running around the clock. That reduced blower electricity usage from 4.3 million kWh to 2.8 million kWh per year and eliminated pH violations. The mixers were also shut off at times in the primary ponds, allowing the operators to lower dissolved oxygen to the spot where the plant could meet effluent standards with the least energy.

“We’re taught that we should keep dissolved oxygen around 2.25 mg/L,” says Ziem. “Now we tend to shoot for 1 to 1.5 mg/L. That’s a good example of seeing what changes you can do with the situation that you have.”

Efficient heating

In 2014, the plant team replaced its old and inefficient propane heaters with 93 percent efficient propane heaters (Modine Manufacturing). “We didn’t just swap out all of them,” Ziem says. “We looked holistically at our facilities. One was in an office that wasn’t occupied all the time, so we put in an electric radiant heater and programmable thermostat. Some others we just turned off.”
One such location was a storage garage where heaters kept a waterline from freezing. The water wasn’t used in winter, so the line was closed and drained, and the heaters turned off. Thermostats were reset from 68 to 50 degrees in the UV disinfection building and a pump building, which were unoccupied. These measures cut propane use from 11,000 gallons to 5,500 gallons per year.

A year later, the plant added 246 more solar panels (69 kW) from Creative Energies to power a pumping facility. That brought solar capacity to 261 kW. “With all the solar we’ve added, of our three main facilities, two are net zero; we produce more electricity than those buildings use.”

The plant also revisited the Triton blowers added five years before. Their SCADA-connected dissolved oxygen sensors in lagoons had to be cleaned every two days from a rowboat. “We ended up not using them, and I felt we were missing a good opportunity to understand what happens with DO throughout the day,” Ziem says.

The sensors were moved to the diversion structures between ponds, where less algae grows and the sensors can be accessed on foot. The SCADA system was updated to track DO every minute in real time. “We can now really understand what happens with dissolved oxygen,” Ziem says. “It really skyrockets in the afternoon.”

Taking chances

Ziem understands that lagoon systems with long detention times are forgiving, so he’s not afraid to experiment. “It’s kind of trial and error,” he says. “I can look at a graph and see what we did and what happened. You can always turn stuff back on and not get yourself in a hole.”

And the 40x20 Initiative? That was met in 2014. As of last year, the 36-year-old plant was treating each gallon 70 percent more efficiently than in 2006. Electricity use has been reduced by 4.5 million kWh per year. “We’re between $50,000 and $70,000 a year that we’re not spending on electricity and propane,” Ziem says.

His new objective is a completely net-zero plant, getting all energy from on-site sources. There’s a long way to go, but he will keep looking.